Increasing concern with soil and groundwater contamination and governmental mandated requirements to clean up hazardous waste sites have created a need for cost effective systems and methods for determining the characterization of subsurface environments. In response to such needs, soil penetrating probes have been developed. Soil penetrating probes generally comprise a tube having a tapered tip which is forced down into the ground. Instrumentation in the tube detects various properties of the surrounding geological environment.
U.S. Pat. No. 5,128,882, "DEVICE FOR MEASURING REFLECTANCE AND FLUORESCENCE OF IN-SITU SOIL," describes a soil penetrating probe having an optical fiber, a light source within the interior of the probe, and a transparent window which provides a light port into and out of the probe. Light passes through the transparent window to irradiate the surrounding soil immediately outside of the window as the probe passes through the soil. The irradiated soil reflects light back through the window whereupon the reflected light is collected by a fiber optic link connected to instrumentation on the surface. The collected light then is subjected to spectroanalysis for determining the chemical composition of the soil, particularly with regard to soil contamination. This system only detects the spectral characteristics of the surrounding environment; It cannot provide optical images. Therefore, information such as the porosity and grain size of surrounding soils are not discernible from the type of information provided through spectral analysis. However, porosity and grain size are important characteristics because they are important variables that control the transport of contaminants in soil.
Another soil penetrating probe system is described in U.S. Pat. No. 5,123,492, "METHOD AND APPARATUS FOR INSPECTING SUBSURFACE ENVIRONMENTS." This system includes a soil penetrating probe having a clear tube in which is suspended a video camera linked to the surface. A significant limitation of this system is that because the camera freely swings within the transparent tube, the focus of the camera with respect to the surrounding geological features is constantly changing and cannot be controlled. Furthermore, the system does not provide any means for illuminating the surrounding subsurface environment other than from ambient light which may happen to filter from the surface down through the tube.
Therefore, a continuing need exists for a system which can provide clear, sharply focused optical images of subsurface geological environments.